Anodizing of shape memory materials

ABSTRACT

Anodizing of a shape memory material product or part includes polishing the shape memory material product or part, thereby producing a polished shape memory material product or part, and then anodizing the polished shape memory material product or part. The polishing of the shape memory material product or part includes mechanical polishing or electrochemical polishing. The electrochemical polishing includes placing the shape memory material product or part in an electrolyte and applying a voltage to the shape memory material product or part for a predetermined time. The anodizing of the polished shape memory material product or part includes placing the polished shape memory material product or part in an electrolyte and applying a voltage to the polished shape memory material product or part for a predetermined time period.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates generally to applying an outer layer toshape memory materials and, more particularly, but not way oflimitation, to anodizing shape memory materials such as Nitinol.

2. Description of the Related Art

Anodizing of metals and metal alloys produces useful benefits includingan outer layer that provides protection and an application of color foruse in color coding of parts. While many metals and metal alloys may beanodized, certain shape memory materials such as Nitinol, which is analloy containing substantially equal mixtures of nickel and titanium,cannot be anodized using standard anodizing processes due to its highnickel content. Nitinol products, such as Nitinol medical implants,therefore are not anodized and thus do not incorporate a protectiveouter layer. Moreover, Nitinol products are not color anodized such thatthe Nitinol products may be color coded for product identification,aesthetics, and quality control.

Accordingly, anodizing of shape memory materials and, in particular,Nitinol will beneficially create Nitinol products that incorporate anouter layer and that may be color coded for product identification,aesthetics, and quality control.

SUMMARY OF THE INVENTION

In accordance with the present invention, a shape memory materialproduct or part is anodized as follows. The shape memory materialproduct or part is polished, thereby producing a polished shape memorymaterial product or part. The polished shape memory material product orpart then is anodized.

The polishing of the shape memory material product or part includesmechanical polishing thereof. The mechanical polishing includes but isnot limited to paste polishing, polishing with emery paper, or abrasiveblasting.

The polishing of the shape memory material product or part includeselectrochemical polishing thereof. The electrochemical polishingincludes placing the shape memory material product or part in anelectrolyte and applying a voltage to the shape memory material productor part for a predetermined time period. The voltage for theelectrochemical polishing is an anodic voltage between 10V and 60V. Thepredetermined time period for the electrochemical polishing includes butis not limited to between 1 and 60 seconds. Applying the voltage for theelectrochemical polishing includes placing a cathode in the electrolytewith the shape memory material product or part therebetween, connectinga negative terminal of a voltage source with the cathode, and connectinga positive terminal of the voltage source with the shape memory materialproduct or part.

The anodizing of the polished shape memory material product or partincludes placing the polished shape memory material product or part inan electrolyte and applying a voltage to the polished shape memorymaterial product or part for a predetermined time period. Theelectrolyte for the anodizing includes phosphoric acid, acetic acid,sulphuric acid, or mixtures thereof in a concentration between 0.1% and5% total volume of the electrolyte. The electrolyte for the anodizingincludes distilled water as a remainder thereof. The voltage for theanodizing is an anodic voltage between 10V and 40V. The predeterminedtime period for the anodizing includes but is not limited to between 1and 120 seconds. Applying the voltage for the anodizing includes placinga cathode in the electrolyte adjacent the polished shape memory materialproduct or part, connecting a negative terminal of a voltage source withthe cathode, and connecting a positive terminal of the voltage sourcewith the shape memory material product or part. As an illustration, avoltage for the anodizing between 29V and 31V and a predetermined timeperiod for the anodizing of 120 seconds produces a gold hue on thepolished shape memory material product or part, whereas a voltage forthe anodizing between 24V and 26V and a predetermined time period forthe anodizing of 120 seconds produces a blue hue on the polished shapememory material product or part.

It is therefore an object of the present invention to facilitate theanodizing of a shape memory material product or part.

It is a further object of the present invention to facilitate theanodizing of a shape memory material product or part through a polishingof the shape memory material product or part prior to the anodizingthereof.

Still other objects, features, and advantages of the present inventionwill become evident to those of ordinary skill in the art in light ofthe following. Also, it should be understood that the scope of thisinvention is intended to be broad, and any combination of any subset ofthe features, elements, or steps described herein is part of theintended scope of the invention.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram illustrating electrochemical polishing of ashape memory material industrial or medical product or part.

FIG. 2 is a block diagram illustrating anodizing of the shape memorymaterial industrial or medical product or part.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

As required, detailed embodiments of the present invention are disclosedherein; however, it is to be understood that the disclosed embodimentsare merely exemplary of the invention, which may be embodied in variousforms. Figures are not necessarily to scale, and some features may beexaggerated to show details of particular components or steps.

Shape memory materials such as Nitinol, due to their superelastic ortemperature dependent shape changing properties, include many industrialand medical uses. Illustratively, Nitinol, which is an alloy containingsubstantially equal mixtures of nickel and titanium, is utilized in golfclub inserts, frames for glasses, cell phone antennae, springs,temperature controls, stents, orthodontic equipment, and the like, and,in particular, orthopedic implants. Nitinol orthopedic implants areimportant in affixing bone, bones, or bone pieces to promote a healingthereof due to their ability to transition between a natural shape andan insertion shape. Nitinol orthopedic implants when deformed from theirnatural shapes to their insertion shapes store energy deliverable tobone, bones, or bone pieces. In accordance with their manufacture fromshape memory materials, Nitinol orthopedic implants begin in theirnatural shapes, are transitionable to their insertion shapes, and, onceimplanted in bone, bones, or bone pieces, attempt to transition fromtheir insertion shapes to their natural shapes whereby the Nitinolorthopedic implants deliver the energy stored therein to the bone,bones, or bone pieces in order to affix the bone, bones, or bone piecesand promote a healing thereof.

Nitinol industrial and medical products and parts such as Nitinolorthopedic implants cannot be anodized using standard anodizingprocesses due to their high nickel content although Nitinol industrialand medical products and parts would benefit from anodizing.Illustratively, anodized Nitinol industrial and medical products andparts such as Nitinol orthopedic implants would include an outer layercapable of providing protection and, if color anodized, could be colorcoded for product identification, aesthetics, and quality control.Moreover, with respect to Nitinol orthopedic implants, an anodizedNitinol orthopedic implant would include an outer layer due to processchanges at its surface layer such that the anodized Nitinol orthopedicimplant becomes more biocompatible for patients with nickel allergiesdue to the outer layer that forms a protective barrier between thenickel of the Nitinol orthopedic implant and the patients experiencingnickel allergies.

Anodizing shape memory materials, and, in particular, the shape memorymaterial Nitinol, includes a preparation step involving polishing of theNitinol employing a chemical/electrochemical polishing technique or amechanical polishing technique including but not limited to pastepolishing, polishing with emery paper, and abrasive blasting with asuitable abrasive media such as sand. Polishing the Nitinol prepares itssurface such that the Nitinol is compatible for application of ananodizing technique that generates an oxide on its surface. Moreparticularly, polishing the Nitinol removes from its surface residualoxides that may interfere with the anodizing technique. After polishing,the Nitinol exhibits a generally bright finish on its surface indicatingresidual oxides have been removed.

After polishing the Nitinol, an anodizing step generates an oxide on thesurface of the Nitinol to form an outer layer that may include aspecific color for product identification, aesthetics, and qualitycontrol. In the preferred embodiment, the thickness of the oxide layermay be between 10 nm (nanometers) and 200 nm (nanometers). Moreparticularly, in anodizing the Nitinol, the Nitinol forms an anode forapplication of an anodizing technique, which may include the Nitinolbeing fixtured to a titanium rack for electrical contact. The cathodefor the anodizing technique is any suitable metal such as stainlesssteel that typically includes a larger surface area than the anode,which, in the preferred embodiment is the Nitinol. The electrolyte forthe anodizing technique is any suitable electrolyte used in anodizingincluding but not limited to an electrolyte of phosphoric acid anddistilled water with the phosphoric acid in a concentration between 0.5%and 5% total volume of the electrolyte and the remainder of theelectrolyte consisting of the distilled water. Other electrolytes mayinclude sulfuric acid or acetic acid in distilled water in similarconcentration ranges to the phosphoric acid and distilled water. Theanodizing technique includes applying an anodic voltage between 20 V and40 V for a predetermined time period including but not limited tobetween 1 second and 120 seconds, depending on the size of the Nitinolto be anodized and the current limitation of the voltage source. Theelectrolyte may be stirred during application of the anodic voltagealthough stirring of the electrolyte is not a necessity. During theanodizing technique, the temperature of the electrolyte is maintainedbetween 68° F./20° C. and 77° F./25° C. utilizing a water bath, althougha higher or lower temperature may produce a successful anodized layer onthe Nitinol. Upon the expiration of the predetermined time period, theNitinol will include a homogenous and adherent outer layer of oxide witha thickness between 10-200 nm. Moreover, depending upon the voltagelevel applied at the anode, the Nitinol will be colored whereby thecolors range among blue and gold. As an illustration, a voltage levelbetween 24V and 26V will produce a blue hue on the Nitinol, and avoltage level between 29V and 31V will produce a gold hue on theNitinol.

In order to illustrate the present invention and aid in theunderstanding thereof, the following example of anodizing a shape memorymaterial industrial or medical product or part and, in particular, aNitinol orthopedic implant is provided. The Nitinol implant ismechanically polished until the Nitinol implant exhibits a desired levelof polishing using one of the following techniques including but notlimited to paste polishing, polishing with emery paper, and abrasiveblasting with a suitable abrasive media such as sand. Illustratively,the Nitinol implant undergoes fine polishing employing emery paper untila mirror finish is achieved.

Alternatively, as illustrated in FIG. 1, a Nitinol implant 10 may beelectrochemically polished. An electrolyte 11 is prepared and thenplaced in a container 12 suitable to hold the electrolyte 11. Theelectrolyte 11 for the electrochemical polishing technique is anysuitable electrolyte used in electrochemical polishing including but notlimited to an electrolyte containing methanesulfonic acid in aconcentration range of 75%-100% and, if included, sulfuric acid in aconcentration range of 2.5%-10%, whereby the density of the electrolyteis 1.5 g/cm³ at 68° F./20° C. with a pH between 0-1. In a particularexample, the electrolyte 11 may be a commercially available electrolyteused in electrochemical polishing such as the electrolyte sold byElpoChem AG, Chriesbaumstr. 4, CH-8064 Volketswil, Switzerland, underthe Trade name ElpoLux TI-med. A cathode 13 for the electrochemicalpolishing technique, which may be any suitable metal such as stainlesssteel, is submerged in the electrolyte 11 and connected to a voltagesource 14 at its negative terminal 15. The Nitinol implant 10 issubmerged in the electrolyte 11 between the cathode 13 and connected tothe voltage source 14 at its positive terminal 16 thereby forming ananode 17 for application of the electrochemical polishing technique,which may include the Nitinol implant 10 being fixtured to a titaniumrack for electrical contact. In the electrochemical polishing technique,the cathode 13 typically includes a larger surface area than the anode17. The electrochemical polishing technique includes utilizing thevoltage source 14 to apply an anodic voltage between 10 V and 60 V and,in particular, an anodic voltage of 25 V for a blue color and 30 V forgold color. The anodic voltage is applied for a predetermined timeperiod of between 1 and 60 seconds and, in particular, a time period of10 seconds. The predetermined time period depends on the ability of thevoltage source 14 to supply current and the surface area of the Nitinolimplant 10 whereby the predetermined time period increases as the sizeof the Nitinol implant 10 increases. The electrolyte 11 may be stirredduring application of the anodic voltage although stirring of theelectrolyte 11 is not a necessity. During the electrochemical polishingtechnique, the temperature of the electrolyte is maintained between 68°F./20° C. and 77° F./25° C. utilizing a water bath, although a higher orlower temperature may produce a successful anodized layer on the Nitinolimplant 10. The temperature could also be outside this range and producea color anodized layer. Upon the expiration of the predetermined timeperiod, the Nitinol implant 10 is polished and its surface preparedthrough a removal of residual oxides such that the Nitinol implant 10 iscompatible for application of an anodizing technique whereby an oxidemay be generated on its surface.

After polishing the Nitinol implant 10, anodizing of the Nitinol implant10 as illustrated in FIG. 2 generates an oxide on the surface of theNitinol implant 10 to form an outer layer that is protective and mayinclude a specific color for product identification, aesthetics, andquality control. An electrolyte 20 is prepared and then placed in acontainer 21 suitable to hold the electrolyte 20. The electrolyte 20 forthe anodizing technique is any suitable electrolyte used in anodizingincluding but not limited to an electrolyte of phosphoric acid, aceticacid, sulphuric acid, or mixtures thereof and distilled water with thephosphoric acid, acetic acid, sulphuric acid, or mixtures thereof in aconcentration between 0.1% and 5% total volume of the electrolyte andthe remainder of the electrolyte consisting of the distilled water. Moreparticularly, the electrolyte 20 is an electrolyte with phosphoric acidin a concentration of 0.5% total volume of the electrolyte with theremainder consisting of distilled water. A cathode 22 for the anodizingtechnique, which may be any suitable metal such as stainless steel, issubmerged in the electrolyte 20 and connected to a voltage source 23 atits negative terminal 24. The Nitinol implant 10 is submerged in theelectrolyte 20 adjacent the cathode 22 and connected to the voltagesource 23 at its positive terminal 25 thereby forming an anode 26 forapplication of the anodizing technique, which may include the Nitinolimplant 10 being fixtured to a titanium rack for electrical contact. Inthe anodizing technique, the cathode 22 typically includes a largersurface area than the anode 26. The anodizing technique includesutilizing the voltage source 23 to apply an anodic voltage of between 10V and 40 V and, in particular, an anodic voltage of 25 V to produce ablue color and an anodic voltage of 30 V to produce a gold color. Theanodic voltage is applied for a predetermined time period of between 1and 120 seconds to produce the blue or gold color and, in particular,for a time period of 120 seconds. The electrolyte 20 may be stirredduring application of the anodic voltage although stirring of theelectrolyte 20 is not a necessity. During the anodizing technique, thetemperature of the electrolyte is maintained between 68° F./15° C. and95° F./35° C. utilizing a water bath. Upon the expiration of thepredetermined time period, the Nitinol implant 10 will include ahomogenous and adherent outer layer of oxide with a thickness between10-200 nm and, in particular, 90 nm for a gold color. Moreover,depending upon the voltage level applied at the anode, the Nitinol willbe colored whereby the colors range among gold and blue. As anillustration, a voltage level between 29 V and 31 V will produce a goldhue on the Nitinol, whereas a voltage level between 24V and 26 V willproduce a blue hue on the Nitinol. In the foregoing specific example,the anodic voltage of 30 V applied for 120 seconds produces bright goldon the Nitinol implant 10. The Nitinol implant 10 is disconnected fromthe voltage source 23 and removed from the electrolyte 20 whereby theNitinol implant 10 includes an outer layer capable of providingprotection as well as a color suitable to provide productidentification, aesthetics, and quality control. Moreover, the anodizedNitinol implant 10 would include an outer layer due to process changesat its surface layer such that the anodized Nitinol implant 10 becomesmore biocompatible for patients with nickel allergies due to the outerlayer that forms a protective barrier between the nickel of the Nitinolimplant 10 and the patients experiencing nickel allergies.

Although the present invention has been described in terms of theforegoing preferred embodiment, such description has been for exemplarypurposes only and, as will be apparent to those of ordinary skill in theart, many alternatives, equivalents, and variations of varying degreeswill fall within the scope of the present invention. That scope,accordingly, is not to be limited in any respect by the foregoingdetailed description; rather, it is defined only by the claims thatfollow.

1. A method of anodizing a shape memory material product or part,comprising: polishing the shape memory material product or part, therebyproducing a polished shape memory material product or part; andanodizing the polished shape memory material product or part.
 2. Themethod of anodizing a shape memory material product or part according toclaim 1, wherein polishing the shape memory material product or partcomprises mechanical polishing of the shape memory material product orpart.
 3. The method of anodizing a shape memory material product or partaccording to claim 2, wherein the mechanical polishing comprises one ofpaste polishing, polishing with emery paper, and abrasive blasting. 4.The method of anodizing a shape memory material product or partaccording to claim 1, wherein polishing the shape memory materialproduct or part comprises electrochemical polishing of the shape memorymaterial product or part.
 5. The method of anodizing a shape memorymaterial product or part according to claim 4, wherein theelectrochemical polishing comprises: placing the shape memory materialproduct or part in an electrolyte; and applying a voltage to the shapememory material product or part for a predetermined time period.
 6. Themethod of anodizing a shape memory material product or part according toclaim 5, wherein the voltage for the electrochemical polishing isbetween 10V and 60V and the predetermined time period for theelectrochemical polishing is between 1 and 60 seconds.
 7. The method ofanodizing a shape memory material product or part according to claim 5,wherein applying a voltage for the electrochemical polishing comprises:placing a cathode in the electrolyte with the shape memory materialproduct or part therebetween; connecting a negative terminal of avoltage source with the cathode; and connecting a positive terminal ofthe voltage source with the shape memory material product or part. 8.The method of anodizing a shape memory material product or partaccording to claim 7, wherein the voltage for the electrochemicalpolishing is an anodic voltage between 10V and 60V and the predeterminedtime period for the electrochemical polishing is between 1 and 60seconds.
 9. The method of anodizing a shape memory material product orpart according to claim 1, wherein anodizing the polished shape memorymaterial product or part comprises: placing the polished shape memorymaterial product or part in an electrolyte; and applying a voltage tothe polished shape memory material product or part for a predeterminedtime period.
 10. The method of anodizing a shape memory material productor part according to claim 9, wherein the electrolyte for the anodizingcomprises: one of phosphoric acid, acetic acid, sulphuric acid, andmixtures thereof in a concentration between 0.1% and 5% total volume ofthe electrolyte; and distilled water, whereby a remainder of theelectrolyte consists of the distilled water.
 11. The method of anodizinga shape memory material product or part according to claim 9, whereinthe voltage for the anodizing is between 10V and 40V and thepredetermined time period for the anodizing is between 1 and 120seconds.
 12. The method of anodizing a shape memory material product orpart according to claim 9, wherein a voltage for the anodizing between29V and 31V and a predetermined time period for the anodizing of 120seconds produces a gold hue on the polished shape memory materialproduct or part.
 13. The method of anodizing a shape memory materialproduct or part according to claim 9, wherein a voltage for theanodizing between 24V and 26V and a predetermined time period for theanodizing of 120 seconds produces a blue hue on the polished shapememory material product or part.
 14. The method of anodizing a shapememory material product or part according to claim 9, wherein applying avoltage for the anodizing comprises: placing a cathode in theelectrolyte adjacent the polished shape memory material product or part;connecting a negative terminal of a voltage source with the cathode; andconnecting a positive terminal of the voltage source with the shapememory material product or part.
 15. The method of anodizing a shapememory material product or part according to claim 14, wherein thevoltage for the anodizing is an anodic voltage between 10V and 40V andthe predetermined time period for the anodizing is between 1 and 120seconds.
 16. A method of anodizing a shape memory material product orpart, comprising: polishing the shape memory material product or part,thereby producing a polished shape memory material product or part,comprising: placing the shape memory material product or part in anelectrolyte, and applying a voltage to the shape memory material productor part for a predetermined time; and anodizing the polished shapememory material product or part, comprising: placing the polished shapememory material product or part in an electrolyte, and applying avoltage to the polished shape memory material product or part for apredetermined time period.
 17. The method of anodizing a shape memorymaterial product or part according to claim 16, wherein the voltage forthe polishing is between 10V and 60V and the predetermined time periodfor the polishing is between 1 and 60 seconds.
 18. The method ofanodizing a shape memory material product or part according to claim 16,wherein the electrolyte for the anodizing comprises: one of phosphoricacid, acetic acid, sulphuric acid, and mixtures thereof in aconcentration between 0.1% and 5% total volume of the electrolyte; anddistilled water, whereby a remainder of the electrolyte consists of thedistilled water.
 19. The method of anodizing a shape memory materialproduct or part according to claim 16, wherein the voltage for theanodizing is between 10V and 40V and the predetermined time period forthe anodizing is between 1 and 120 seconds.
 20. A method of anodizing ashape memory material product or part, comprising: mechanicallypolishing the shape memory material product or part, thereby producing apolished shape memory material product or part; and anodizing thepolished shape memory material product or part, comprising: placing thepolished shape memory material product or part in an electrolyte, andapplying a voltage to the polished shape memory material product or partfor a predetermined time period.
 21. The method of anodizing a shapememory material product or part according to claim 20, wherein theelectrolyte for the anodizing comprises: one of phosphoric acid, aceticacid, sulphuric acid, and mixtures thereof in a concentration between0.1% and 5% total volume of the electrolyte; and distilled water,whereby a remainder of the electrolyte consists of the distilled water.22. The method of anodizing a shape memory material product or partaccording to claim 20, wherein the voltage for the anodizing is between10V and 40V and the predetermined time period for the anodizing isbetween 1 and 120 seconds.